Epidermal growth factor (EGF), a polypeptide consisting of 53 amino acid residues, is produced by the mouse submandibular gland. EGF has diverse biological actions influencing proliferation, differentiation, and functional activities of various types of cells. However, the physiological role of EGF has not been well-defined. Our previous studies indicate that submandibular gland-derived EGF plays a role in the development of the mammary gland during pregnancy and mammary tumorigenesis in female mice. By contrast, the physiological role of EGF in males is not clear, despite knowledge that the concentration of EGF in the submandibular gland and plasma of male mice is much higher than that of females. In males, the production of EGF increases in parallel with sexual maturation, and androgens stimulate its production in the submandibular gland. We have examined the effect of sialoadenectomy and EGF replacement on several parameters of male reproductive function, including sperm production. Our results indicate that sialoadenectomy decreases the amount of circulating EGF to an undetectable level, but does not affect the circulating levels of testosterone and FSH. The number of mature sperm in the epididymis decreases by about 55%; the number of spermatids in the testis decreases 40-50%; and the number of spermatocytes increases about 20%. Administration of EGF to sialoadenectomized mice completely corrected both the sperm content of the epididymis and the number of spermatids in the testis. Thus, EGF may serve a role in male reproduction by stimulating the meiotic phase of spermatogenesis through a submandibular glandtestis axis. The most important question in the study of actions of polypeptide hormones deals with identifying the steps in the transduction chain. We examined the effect of EGF on the membrane potential and ion channels of mammary epithelial cells by electrophysiological techniques. These studies reveal that EGF induces a hyperpolarizing response by stimulating the Ca2-dependent K+ channel. This response may be closely related to the mechanisms responsible for the mitogenic action of EGF.